The invention relates to a fifth wheel for the coupling of the tractor of an articulated truck with a truck trailer comprising a wheel plate, a king pin with an inner bore and with an outer coupling or engaging surface as well as with connections for linking electric and pneumatic supply lines between the tractor of an articulated truck and the truck trailer, wherein the supply lines of the tractor of the articulated truck lead to a male connector of a supply unit and the supply lines from a female connector in the interior of the kingpin to the designated places on the truck trailer, the male connector being extendable from the supply part and retractable into the female connector, and wherein the male connector can rotate with respect to the female connector.
Such a fifth wheel is known (EP 816 211-A2), however, it has considerable drawbacks insofar, as due to the arrangement of the individual lines side by side in the kingpin, the latter must be bored to that extent that the lines and the line connections can be received within its interior, but the tensile strength has been decreased so far that it is not suitable for use in practice.
In a different known kingpin design (EP 058 075-A1), two concentric pressurised air lines are located within the interior of the kingpin and of the male connector. However, electrical lines are not provided there, rather, for example, the blinker lights of the truck trailer should be actuated through a battery on the trailer truck and through a radio frequency transmission.
In a further known coupling system (U.S. Pat. No. 3,181,887), a pressurised air line is lead through the interior of the kingpin. Flexible electrical lines are lead within the kingpin as well as within the male connector of the supply unit to co-operating pins and slide rings. However, such contact connections do not result in reliable electrical connections and, furthermore, are not safe in operation due to possible contamination.
In a known vehicle coupling device (U.S. Pat. No. 3,428,334), two pressurised air lines are lead inside the kingpin, wherein electrical connections are implemented via co-operating sliders and slide rings arranged on matching conical surfaces. However, the electrical connections are not sufficiently safe in operation. This is supplemented by the fact that the kingpin has been made weak by the selected type of connection such that the coupling device is not usable in practice.
The invention is based on the task to design a fifth wheel of the type named above such that the kingpin has such a strength that the usually required operating license of the admission authorities can be issued and electrically faultless connections between male connector and female connector are possible.
This is achieved by the features indicated in the characterising part of the claim.
In the fifth wheel according to the invention, all connections, the pneumatic as well as the electric connections, are implemented by bushes coaxially aligned and fit into one another. Bushes fit into one another have a relatively large effective surface, which results in faultless contacts in the electric lines.
The engaging surfaces of these bushes fit into one another lie in an area arranged radially inside with respect to the coupling or engagement surface of the kingpin, that is an area, where during shunting of the trailer receiver by the tractor of the articulated truck little or hardly any relative movements occur.
The bushes for all lines are arranged coaxially with respect to one another such that the pressurised air lines are connected with each other on the outside with regard to the electrical lines. This make it possible to clean the areas of the electrical connections by means of pressurised air blasts before the insertion of the male connector into the female connector. This is an advantage, which cannot be disregarded in the harsh operating conditions.
Finally, the radially largest bush or the inner bore surface of the kingpin are dimensioned such that their diameter is less than half the outer diameter of the coupling or engaging surface of the kingpin. With this dimensioning it can be achieved that the mechanical demands made on the kingpin are met.